Purification and recovery of a nucleic acid having a particular base sequence is one of the basic techniques that are important in the field of genetic engineering. In the purification and recovery of a nucleic acid having a particular base sequence, the formation of a hybrid (hybridization) with a nucleic acid probe having a base sequence that is complementary to the particular sequence, has been long used as a fundamental principle which allows specific recognition of a particular base sequence (see, for example, Non-Patent Document 1).
However, under the actual conditions for the hybrid formation, it is difficult to induce the association with the nucleic acid probe molecule only by means of the nucleic acid of the target base sequence that hybridizes as a complete complementary chain. That is, it is known that even a nucleic acid having a non-target base sequence that is incomplete as a complementary chain, undergoes incomplete hybridization including certain mismatches, and association with the nucleic acid probe molecule occurs. Such an unintended association with the nucleic acid probe (error) will appear as a noise (impurity) in the subsequent recovery stage. In order to increase the specificity of detection so as to prevent the appearance of this noise, it is necessary to eliminate incomplete hybridization.
On the other hand, in order to reduce the noise (impurity), the treatment may be carried out under the conditions which do not allow incomplete hybridization as far as possible; however, under such conditions, the intended hybridization is also unstabilized. As a result, the recovery rate of a target nucleic acid is decreased.
However, the discrimination by hybridization makes use of the difference in the thermal stability in an equilibrium system, and the difference between the complete hybridization and the incomplete hybridization is merely a difference in the thermal stability. Therefore, the conditions appropriate for discriminating the two vary with the target base sequence, and even under appropriate conditions, the conditions that alter the thermal stability act equally on both. Even under the experimental conditions in which strict temperature management has been conducted, this fact does not change. That is, as long as only the difference in the thermal stability of hybridization in an equilibrium system is used as the principle of discrimination of the two, even if an experiment is performed under the experimental conditions with the conditions of temperature management or the like strictly set, a certain noise (impurities) had to be put up with by making compromise in the balance between the degree of purification and the recovery rate.
Moreover, in recent years, there is a demand for a technology intended to achieve the purification and recovery of a nucleic acid having a single-base-substituted base sequence, for the purpose of new drug development or genetic diagnosis. Particularly, a technology for typing single nucleotide polymorphism of DNA is under high expectation in the field of medical diagnosis. Therefore, there is a special demand for a technology for purification and recovery, which achieves a good balance between high sequence specificity to the extent capable of discriminating single base substitution, and a practically useful recovery rate.
In recent years, there is also a demand for a technology intended to achieve the purification and recovery of an RNA that is not translated, which is generally referred to as non-coding RNA (ncRNA). This ncRNA includes one group called microRNA (miRNA) because of the small size of the molecules, and furthermore, a significant portion of the molecules which have been traditionally regarded as mRNA simply because the molecules have polyA and is frequently subjected to splicing, is said to belong to a group called mRNA-like ncRNA. However, since these RNAs exist in many species, with small numbers of molecules, and also since the RNAs are susceptible to degradation and short-lived, purification and recovery thereof must be carried out in a very short time. For this reason, a technology for sequence-specific purification and recovery of RNA, which can be carried out in a very short time, is especially in demand.    Non-Patent Literature 1: Lambert, K. N., Williamson, V. M. Nucleic Acids Res., 1993, 21, pp. 775-776.